Seasonal selectivity of Magellanic horned owl (Bubo magellanicus) on rodents

This study examines prey selection by Magellanic horned owls (Bubo magellanicus) in an ecotonal steppe area of northwestern Argentine Patagonia, and analyzes morphological and behavioral traits of the owls main rodent prey. The owls diet was studied for two years, along with field estimates of rodent abundance. The frequency distribution of rodents was significantly different from that estimated from trapping, indicating that Magellanic horned owl behaved as a selective predator. Eligmodontia morgani and Abrothrix xanthorhinus, the smallest species inhabiting open areas, were consumed in lower proportion than their occurrence estimated from the trapped sample, whereas the larger Abrothrix longipilis and Oligoryzomys longicaudatus, which inhabited bushy habitats, were eaten in a greater proportion than their estimated abundance. It is suggested that distinctive morphological and behavioral characteristics among prey interacting with the owl hunting strategy, accounted for their differential vulnerability to predation.     

Rapid sequence turnover at an intergenic locus in Drosophila

Closely related species of Drosophila tend to have similar genome sizes. The strong imbalance in favor of small deletions relative to insertions implies that the unconstrained DNA in Drosophila is unlikely to be passively inherited from even closely related ancestors, and yet most DNA in Drosophila genomes is intergenic and potentially unconstrained. In an attempt to investigate the maintenance of this intergenic DNA, we studied the evolution of an intergenic locus on the fourth chromosome of the Drosophila melanogaster genome. This 1.2-kb locus is marked by two distinct, large insertion events: a nuclear transposition of a mitochondrial sequence and a transposition of a nonautonomous DNA transposon DNAREP1_DM. Because we could trace the evolutionary histories of these sequences, we were able to reconstruct the length evolution of this region in some detail. We sequenced this locus in all four species of the D. melanogaster species complex: D. melanogaster, D. simulans, D. sechellia, and D. mauritiana. Although this locus is similar in size in these four species, less than 10% of the sequence from the most recent common ancestor remains in D. melanogaster and all of its sister species. This region appears to have increased in size through several distinct insertions in the ancestor of the D. melanogaster species complex and has been shrinking since the split of these lineages. In addition, we found no evidence suggesting that the size of this locus has been maintained over evolutionary time; these results are consistent with the model of a dynamic equilibrium between persistent DNA loss through small deletions and more sporadic DNA gain through less frequent but longer insertions. The apparent stability of genome size in Drosophila may belie very rapid sequence turnover at intergenic loci.     

Enhancement of the Influenza A Hemagglutinin (HA)-Mediated Cell-Cell Fusion and Virus Entry by the Viral Neuraminidase (NA)

Background

The major role of the neuraminidase (NA) protein of influenza A virus is related to its sialidase activity, which disrupts the interaction between the envelope hemagglutin (HA) protein and the sialic acid receptors expressed at the surface of infected cells. This enzymatic activity is known to promote the release and spread of progeny viral particles following their production by infected cells, but a potential role of NA in earlier steps of the viral life cycle has never been clearly demonstrated. In this study we have examined the impact of NA expression on influenza HA-mediated viral membrane fusion and virion infectivity.

Methodology/Principal Findings

The role of NA in the early stages of influenza virus replication was examined using a cell-cell fusion assay that mimics HA-mediated membrane fusion, and a virion infectivity assay using HIV-based pseudoparticles expressing influenza HA and/or NA proteins. In the cell-cell fusion assay, which bypasses the endocytocytosis step that is characteristic of influenza virus entry, we found that in proper HA maturation conditions, NA clearly enhanced fusion in a dose-dependent manner. Similarly, expression of NA at the surface of pseudoparticles significantly enhanced virion infectivity. Further experiments using exogeneous soluble NA revealed that the most likely mechanism for enhancement of fusion and infectivity by NA was related to desialylation of virion-expressed HA.

Conclusion/Significance

The NA protein of influenza A virus is not only required for virion release and spread but also plays a critical role in virion infectivity and HA-mediated membrane fusion.     

Molecular evidence for Pleistocene glacial cycles driving diversification of a North American desert spider, Agelenopsis aperta

The influence of historical climatic vs. geological changes on species diversification patterns was investigated in a widely distributed North American desert spider, Agelenopsis aperta (Araneae: Agelenidae), with particular reference to Pleistocene glacial cycles and earlier patterns of mountain building. Levels of sequence divergence obtained from the mitochondrial gene, cytochrome oxidase I, dated to the Pleistocene, eliminating Rocky Mountain orogeny as a cause of diversification, as orogeny ended 4 million years ago. The results of phylogenetic and network analyses showed the presence of three geographically defined clades, which were consistent with the presence of at least three glacial refugia: (i) east of the Rocky Mountains; (ii) between the Rocky Mountains and Sierra Nevadas; and (iii) west of the Sierra Nevadas. In addition, populations within the Rocky Mountains exhibited significantly lower genetic diversity than populations east of the Rocky Mountains and the haplotypes found within the Rockies were a subset of eastern haplotypes. These patterns suggest that a post-Pleistocene range expansion occurred out of an eastern glacial refugium into the Rocky Mountains. Examination of phylogeographical studies of other North American desert taxa indicated that mountain building explained diversification patterns more effectively for some taxa but Pleistocene climate change was more important for others, including A. aperta.     

Molecular Cloning, Expression Pattern, and Chromosomal Localization of the Human Na–Cl Thiazide-Sensitive Cotransporter (SLC12A3)

Electrolyte homeostasis is maintained by several ion transport systems. Na–(K)–Cl cotransporters promote the electrically silent movement of chloride across the membrane in absorptive and secretory epithelia. Two kidney-specific Na–(K)–Cl cotransporter isoforms are known, so far, according to their sensitivity to specific inhibitors. We have cloned the human cDNA coding for the renal Na–Cl cotransporter selectively inhibited by the thiazide class of diuretic agents. The predicted protein sequence of 1021 amino acids (112 kDa) shows a structure common to the other members of the Na–(K)–Cl cotransporter family: a central region harboring 12 transmembrane domains and the 2 intracellular hydrophilic amino and carboxyl termini. The ex- pression pattern of the human Na–Cl thiazide-sensitive cotransporter (hTSC, HGMW-approved symbol SLC12A3) confirms the kidney specificity. hTSC has been mapped to human chromosome 16q13 by fluorescencein situhybridization. The cloning and characterization of hTSC now render it possible to study the involvement of this cotransport system in the pathogenesis of tubulopathies such as Gitelman syndrome.     

Changes in the miRNA-mRNA Regulatory Network Precede Motor Symptoms in a Mouse Model of Multiple System Atrophy: Clinical Implications

Multiple system atrophy (MSA) is a fatal rapidly progressive α-synucleinopathy, characterized by α-synuclein accumulation in oligodendrocytes. It is accepted that the pathological α-synuclein accumulation in the brain of MSA patients plays a leading role in the disease process, but little is known about the events in the early stages of the disease. In this study we aimed to define potential roles of the miRNA-mRNA regulatory network in the early pre-motor stages of the disease, i.e., downstream of α-synuclein accumulation in oligodendroglia, as assessed in a transgenic mouse model of MSA. We investigated the expression patterns of miRNAs and their mRNA targets in substantia nigra (SN) and striatum, two brain regions that undergo neurodegeneration at a later stage in the MSA model, by microarray and RNA-seq analysis, respectively. Analysis was performed at a time point when α-synuclein accumulation was already present in oligodendrocytes at neuropathological examination, but no neuronal loss nor deficits of motor function had yet occurred. Our data provide a first evidence for the leading role of gene dysregulation associated with deficits in immune and inflammatory responses in the very early, non-symptomatic disease stages of MSA. While dysfunctional homeostasis and oxidative stress were prominent in SN in the early stages of MSA, in striatum differential gene expression in the non-symptomatic phase was linked to oligodendroglial dysfunction, disturbed protein handling, lipid metabolism, transmembrane transport and altered cell death control, respectively. A large number of putative miRNA-mRNAs interaction partners were identified in relation to the control of these processes in the MSA model. Our results support the role of early changes in the miRNA-mRNA regulatory network in the pathogenesis of MSA preceding the clinical onset of the disease. The findings thus contribute to understanding the disease process and are likely to pave the way towards identifying disease biomarkers for early diagnosis of MSA.     

Migration of Naphthalene through Low Organic Content Sandy Soil Columns: Comparison of Unsaturated and Saturated Conditions

The transient transport of naphthalene through low organic matter content soil columns was investigated in different water-saturation and flow conditions. Some parameters were tested as flow rate, column height, and water saturation conditions. The soil was a clayed sandy soil from the Algerian coast near Boumerdes. The organic carbon content was 0.13% and the main mineral components were quartz (88%), clays minerals (7%) and calcite (3%). The height of the packing of the soil column (5.1 cm in diameter) varied from 15 to 40 cm. Simultaneous step injections of inert tracer (calcium chloride) and naphthalene at 10 mg L^?1 were performed. Tracer and naphthalene breakthrough curves (BTCs) were measured continuously by conductimetry and UV – 220 nm, respectively. The BTCs were simulated using the classical mixing cells in series with exchange model (MCE). In unsaturated conditions the comparison of the mean residence time of tracer BTCs with the geometrical pore volume gave us access to average water saturation along the column as a function of height. The higher the soil bed was, the higher the mean water saturation. The comparison of naphthalene distribution coefficients (K_d) in different flow conditions with the theoretical value from the Karickhoff law showed that in saturated conditions the obtained value was close to the theoretical one. In unsaturated conditions, the measured naphthalene K_d's were much lower than the theoretical value and correlated to the water saturation.     

Effects of habitat fragmentation on provisioning rates, diet and breeding success in two species of tit (great tit and blue tit)

The aim of this study was to examine the effects of forest fragmentation on the ability of parent birds to provide their young with an adequate food supply. To examine whether prey population densities of the great tit (Parus major L.) and the blue tit (P. caeruleus L.) vary between study areas in different forest size classes we compared provisioning rates and chick diet and related these parameters to breeding success. We filmed 217 nests over two breeding seasons and collected data on frass fall as a general estimate of caterpillar availability. Nests which were attended by none or one parent only during filming (n = 46) were excluded from the analyses. In both years and for both species feeding rates were highest in the smallest fragments and lowest in the large forest. There was also a suggestion that differences in feeding rates between areas vary between years. We found no consistent tendency for prey size to change with forest size, although both species brought slightly smaller prey items to the nest in the smallest forest fragments and feeding rates correlated negatively with prey size. Caterpillars were the main item fed to nestlings, in both species. We found no evidence to suggest that either frass fall or the proportion of caterpillars in the diet varied with forest size. There was also no correlation between mean frass fall and the total number of caterpillars brought to the nests, in either species. Breeding success, as measured by clutch size, brood size, fledging weight and fledging success, did not differ between the small fragments and the large forest, in either species. There was also no relationship between provisioning rate (as concerns volume of prey fed to nestlings and the quality of chick diet) and breeding success parameters. In conclusion, this study does not suggest suboptimal foraging or breeding conditions in small fragments compared to a nearby large forest, for either species. Received: 23 June 1997 / Accepted: 29 December 1997     

Mental retardation and abnormal skeletal development (Dyggve-Melchior-Clausen dysplasia) due to mutations in a novel,evolutionarily conserved gene

Dyggve-Melchior-Clausen dysplasia (DMC) and Smith-McCort dysplasia (SMC) are similar, rare autosomal recessive osteochondrodysplasias. The radiographic features and cartilage histology in DMC and SMC are identical. However, patients with DMC exhibit significant developmental delay and mental retardation, the major features that distinguish the two conditions. Linkage studies localized the SMC and DMC disease genes to chromosome 18q12-21.1, providing evidence suggesting that they are allelic disorders. Sequence analysis of the coding exons of the FLJ90130 gene, a highly evolutionarily conserved gene within the recombination interval defined in the linkage study, identified mutations in SMC and DMC patients. The affected individuals in two consanguinous DMC families were homozygous for a stop codon mutation and a frameshift mutation, respectively, demonstrating that DMC represents the FLJ90130-null phenotype. The data confirm the hypothesis that SMC and DMC are allelic disorders and identify a gene necessary for normal skeletal development and brain function.